This invention relates to camera shutter control means. Heretofore, there have been known various methods of causing a delay of a shutter aperture closing member by operating a mechanical delay means for controlling the camera shutter exposure period, and they are roughly classed into two types, namely one in which the exposure is started when an operating member is released by shutter release to release an opening member and is ended when a closing member is operated after a delay time provided by a mechanical delaying means, and one in which the exposure period is desirably controlled with opening and closing members adapted to be released without any time relation to each other and with mechanical delaying means having direct effect upon the sole closing member.
The first-mentioned method has a drawback in that the operating stroke of the operating member tends to be large so that the set angle of the shutter tends to be large. Also, since the opening and closing members are released in succession by the operating member, in order to control the exposure period to the shortest period (for instance 1/2,000 second), the opening and closing members have to be released in succession with only a very slight time difference involved. Therefore, steady control cannot be obtained unless the precision of the component parts is sufficiently improved; in extreme cases inversion of their phases is likely to result.
In the second-mentioned method, a greater stroke is required for the closing member. While it is often used for shutters of the type being wound on a drum such as cloth screen focal plane shutters, with increase of the stroke the size of the shutter is usually increased as well and such an increase in size is disadvantageous.
Where gear trains are used as the mechanical delaying means for controlling the exposure period of the camera, the end of accurately controlling the exposure period over a wide range is achieved by arranging such as to vary the resistance ratio in the gear train by such means as an ankle detachably provided in mesh with the gear train or a part thereof.
A switching means for causing engagement or disengagement of part of the gear train or the ankle is constructed such that engagement and disengagement is directly effected by operating a shutter dial. However, where the switching means is reduced in size in accordance with size reduction of the camera, it is extremely difficult to effect the engagement and disengagement directly with the switching means unless the stroke of the member for engagement and disengagement is reduced.